Morphology of nares associated with stereo-olfaction in baleen whales

The sensory mechanisms used by baleen whales (Mysticeti) for locating ephemeral, dense prey patches in vast marine habitats are poorly understood. Baleen whales have a functional olfactory system with paired rather than single blowholes (nares), potentially enabling stereo-olfaction. Dimethyl sulfide (DMS) is an odorous gas emitted by phytoplankton in response to grazing by zooplankton. Some seabirds use DMS to locate prey, but this ability has not been demonstrated in whales. For all 15 extant species of baleen whale, nares morphometrics (imagery from unoccupied aerial systems, UAS) was related to published trophic level indices using Bayesian phylogenetic mixed modelling. A significant negative relationship was found between nares-width and whale trophic level (β = -0.07, Lower 95% CI = -0.12, Upper 95% CI = -0.02), corresponding with a 36% increase in nares-width from highest to lowest trophic level. Thus, species with nasal morphology best suited to stereo-olfaction are more zooplanktivorous. These findings provide evidence that some baleen whale species may be able to localise odorants e.g., DMS. Our results helps direct future behavioural trials of olfaction in baleen whales, by highlighting the most appropriate species to study. This is a research priority, given the potential for DMS-mediated plastic ingestion by whales.须鲸（Mysticeti，须鲸亚目）在广阔海洋生境中定位短暂密集猎物斑块所依赖的感官机制，目前仍未得到充分阐明。须鲸拥有成对而非单个的喷水孔（鼻孔），具备功能性嗅觉系统，这使其可能具备立体嗅觉能力。二甲基硫（Dimethyl sulfide, DMS）是浮游植物在被浮游动物摄食时释放的有气味气体。部分海鸟可利用二甲基硫定位猎物，但鲸类是否具备该能力尚未得到证实。针对现存的全部15种须鲸，本研究采用贝叶斯系统发育混合模型，将鼻孔形态测量数据（源自无人航空系统（Unoccupied Aerial Systems, UAS）的影像）与已发表的营养级指数进行关联分析。研究发现鼻孔宽度与鲸类营养级呈显著负相关（β=-0.07，95%置信区间下限为-0.12，上限为-0.02），从最高营养级到最低营养级，鼻孔宽度增加了36%。因此，鼻腔形态最适配立体嗅觉的须鲸物种，其食性更偏向浮游动物食性。上述研究结果为部分须鲸物种具备定位气味物质（如二甲基硫）的能力提供了证据。本研究结果明确了最适合开展相关研究的物种，可为未来须鲸嗅觉相关行为实验提供指导方向。鉴于鲸类可能通过二甲基硫介导的途径摄入塑料垃圾，该研究方向已成为当前的重点科研议题。